A circuit-breaker pole part can be integrated in a medium-voltage or high-voltage circuit breaker. Medium-voltage circuit-breakers can be rated between 1 and 72 kV of a high current level. These breakers interrupt the current by generating and extinguishing the arc in a vacuum chamber. Modern vacuum circuit-breakers tend to have a longer life time than former air or oil circuit-breakers. Although vacuum circuit-breakers replaced air or oil circuit-breakers. The present disclosure is not only applicable to vacuum circuit-breakers, but also for air or oil circuit-breakers or modern SF6 circuit-breakers having a chamber filled with sulfur hexafluoride gas instead of vacuum.
For actuating a circuit-breaker, usually a magnetic actuator with high force density is used which moves the electrical contacts of an interrupter insert for a purpose of electrical power interruption. Therefore, a mechanical connection between a movable armature of the magnetic actuator and the moveable contact inside the interrupter insert is provided.
The document DE 10 2004 060 274 A1 discloses a method for producing a circuit-breaker pole part for a medium voltage or high voltage circuit-breaker. A vacuum interrupter is embedded in an insulation material and encapsulated with said material. The vacuum interrupter itself can include an insulator housing which can be cylindrical and is closed at the ends in order to form an inner vacuum chamber. The vacuum chamber contains a fixed electrical contact and a corresponding movable contact for an electrical switch. A folding bellows is arranged on the moveable electrical contact and permits a movement of the respective electrical contact over the current feed line within the vacuum chamber. As mentioned, a high vacuum is maintained within the vacuum interrupter in order to quench as rapid as possible the arc produced during a switching-on or a switching-off action.
Such a vacuum interrupter inside the insulating sleeve can be encapsulated by a synthetic material, mostly plastic material, in order to increase the external dielectric strength of the vacuum interrupter insert. Furthermore, the synthetic material serves as a compensation material for the purpose of compensating for different coefficient of thermal expansion between the vacuum interrupter surface and the surrounding insulating sleeve. This additional function of the intermediate layer avoids possible initiation of cracks.
During the manufacturing process of the circuit-breaker pole part two external electrical contacts are mounted in the insulating sleeve in a first step. In a second step, the pre-mounted interrupter insert is dipped into a liquid rubber solution forming the intermediate layer. In a third step, the external insulating sleeve is produced in a plastic injection-moulding process by the vacuum interrupter insert being encapsulated with plastic material. During encapsulating, the vacuum interrupter insert by moulding under a high process temperature the liquid rubber solution vulcanizes and forms the intermediate compensating layer as described above. For the last production step of vulcanizing a heated moulded form is necessary.
The document U.S. 2008/0142485 A1 discloses another method for producing a pole part of a medium-voltage to high-voltage circuit-breaker arrangement. The external insulating sleeve is produced in a plastic injection-moulding process wherein the vacuum chamber is encapsulated by an injection moulding stop. The insulating sleeve can be produced from plastic or a rubber-elastic material. Prior to the plastic embedding of the vacuum-interrupter, it can be encased by an intermediate compensating layer. In order to achieve good adhesion properties, an additional bonding agent can be used. During manufacturing the compensating layer is firstly applied to the vacuum interrupter, which is in further step encapsulated by injection moulding with plastic material and then is provided with further layers of plastic material. A respective number of different injection moulding forms can be specified in order to achieve the multi-layer design.
Without an additional bonding agent a reliable bonding between the different layers is not possible.